[Enhancement] Improve some load channel and delta writer metrics

[wyb]

Why I'm doing:

What I'm doing:

1. add eos related metrics load_channel_add_chunks_eos_total delta_writer_commit_task_total
2. add flush task metric delta_writer_wait_flush_task_total
3. add delta writer commit metrics delta_writer_pk_preload_duration_us delta_writer_txn_commit_duration_us
4. rename pk preload profile

Fixes #issue

What type of PR is this:

• BugFix
• Feature
• Enhancement
• Refactor
• UT
• Doc
• Tool

Does this PR entail a change in behavior?

• Yes, this PR will result in a change in behavior.
• No, this PR will not result in a change in behavior.

If yes, please specify the type of change:

• Interface/UI changes: syntax, type conversion, expression evaluation, display information
• Parameter changes: default values, similar parameters but with different default values
• Policy changes: use new policy to replace old one, functionality automatically enabled
• Feature removed
• Miscellaneous: upgrade & downgrade compatibility, etc.

Checklist:

• I have added test cases for my bug fix or my new feature
• This pr needs user documentation (for new or modified features or behaviors)
  • I have added documentation for my new feature or new function
• This is a backport pr

Bugfix cherry-pick branch check:

• I have checked the version labels which the pr will be auto-backported to the target branch
  • 3.4
  • 3.3
  • 3.2
  • 3.1
  • 3.0

[github-actions]

[Java-Extensions Incremental Coverage Report]

✅ pass : 0 / 0 (0%)

[github-actions]

[FE Incremental Coverage Report]

✅ pass : 0 / 0 (0%)

[github-actions]

[BE Incremental Coverage Report]

✅ pass : 20 / 21 (95.24%)

file detail

	path	covered_line	new_line	coverage	not_covered_line_detail
🔵	be/src/storage/delta_writer.cpp	8	9	88.89%	[647]
🔵	be/src/runtime/load_channel.cpp	5	5	100.00%	[]
🔵	be/src/util/starrocks_metrics.cpp	5	5	100.00%	[]
🔵	be/src/runtime/local_tablets_channel.cpp	2	2	100.00%	[]